diff --git a/src/underworld3/discretisation/discretisation_mesh.py b/src/underworld3/discretisation/discretisation_mesh.py
index f9bc72ad..1566d309 100644
--- a/src/underworld3/discretisation/discretisation_mesh.py
+++ b/src/underworld3/discretisation/discretisation_mesh.py
@@ -1832,6 +1832,19 @@ def _deform_mesh(self, new_coords: numpy.ndarray, verbose=False):
                 if solver is not None and hasattr(solver, "is_setup"):
                     solver.is_setup = False
 
+            # Invalidate caches whose contents become stale when mesh
+            # coordinates change. Matches the cache hygiene already
+            # performed by mesh.adapt() and _legacy_access. Without
+            # these, uw.function.evaluate (and any user code that keys
+            # lookups off _topology_version) can return values
+            # computed against the pre-deform mesh.
+            self._evaluation_hash = None
+            self._evaluation_interpolated_results = None
+            if hasattr(self, '_dminterpolation_cache'):
+                self._dminterpolation_cache.invalidate_all(
+                    reason="mesh deformed")
+            self._topology_version += 1
+
             # Propagate coordinate changes to registered submeshes
             for submesh in self._registered_submeshes:
                 submesh.sync_coordinates_from_parent()
diff --git a/tests/test_0825_deform_mesh_cache_invalidation.py b/tests/test_0825_deform_mesh_cache_invalidation.py
new file mode 100644
index 00000000..f0557851
--- /dev/null
+++ b/tests/test_0825_deform_mesh_cache_invalidation.py
@@ -0,0 +1,91 @@
+"""Regression test for cache invalidation on Mesh._deform_mesh.
+
+After a coordinate change, three mesh-level caches need to be marked
+stale so subsequent lookups recompute against the new geometry:
+
+  - self._evaluation_hash + self._evaluation_interpolated_results
+    (the legacy uw.function.evaluate fast-path cache)
+  - self._dminterpolation_cache (DMInterpolation structures keyed on
+    coord-hash; encode cell residency and reference->physical maps)
+  - self._topology_version (a counter that downstream caches consult)
+
+mesh.adapt() and _legacy_access already invalidate these. Before this
+fix, _deform_mesh did not, leaving a gap where user code that re-uses
+the same coord array across a deformation could hit a stale cache
+built on the pre-deform mesh.
+
+This test warms each cache (by performing an evaluate that populates
+them), then calls _deform_mesh and verifies the caches are cleared
+and the topology version has been bumped.
+"""
+
+import numpy as np
+import pytest
+
+import underworld3 as uw
+
+
+pytestmark = [pytest.mark.level_1, pytest.mark.tier_a]
+
+
+def _build_mesh_with_field():
+    """A small structured-quad mesh plus a scalar field to drive evals."""
+    mesh = uw.meshing.StructuredQuadBox(
+        elementRes=(8, 8),
+        minCoords=(0.0, 0.0),
+        maxCoords=(1.0, 1.0),
+    )
+    s = uw.discretisation.MeshVariable(
+        "S_cache_test", mesh, 1, degree=2, continuous=True)
+    s.data[:, 0] = 1.0  # constant — exact value irrelevant
+    return mesh, s
+
+
+def _warm_caches(mesh, var):
+    """Trigger an evaluate that populates _evaluation_hash and
+    _dminterpolation_cache."""
+    coords = np.asarray(mesh.X.coords, dtype=np.double)
+    # uw.function.evaluate goes through the petsc_interpolate path,
+    # which populates _dminterpolation_cache.
+    _ = uw.function.evaluate(var.sym, coords)
+
+
+def test_topology_version_bumps_on_deform():
+    mesh, s = _build_mesh_with_field()
+    _warm_caches(mesh, s)
+    before = mesh._topology_version
+    coords = np.asarray(mesh.X.coords)
+    perturbed = coords.copy()
+    perturbed[:, 0] += 1.0e-3 * coords[:, 1]
+    mesh._deform_mesh(perturbed)
+    assert mesh._topology_version > before, (
+        "_topology_version should be incremented by _deform_mesh")
+
+
+def test_evaluation_hash_invalidated_on_deform():
+    mesh, s = _build_mesh_with_field()
+    _warm_caches(mesh, s)
+    # uw.function.evaluate may have populated _evaluation_hash
+    coords = np.asarray(mesh.X.coords)
+    perturbed = coords.copy()
+    perturbed[:, 1] += 5.0e-4 * coords[:, 0]
+    mesh._deform_mesh(perturbed)
+    assert mesh._evaluation_hash is None
+    assert mesh._evaluation_interpolated_results is None
+
+
+def test_dminterpolation_cache_invalidated_on_deform():
+    mesh, s = _build_mesh_with_field()
+    _warm_caches(mesh, s)
+    # The cache should have at least one entry after the warm-up evaluate.
+    n_before = len(getattr(
+        mesh._dminterpolation_cache, "_cache", {}))
+    coords = np.asarray(mesh.X.coords)
+    perturbed = coords.copy()
+    perturbed[:, 1] += 1.0e-3 * coords[:, 0]
+    mesh._deform_mesh(perturbed)
+    n_after = len(getattr(
+        mesh._dminterpolation_cache, "_cache", {}))
+    assert n_after == 0, (
+        f"Expected DMInterpolation cache to be empty after deform; "
+        f"got {n_after} entries (before deform: {n_before})")