  We prove that continuous Hochschild and cyclic homology satisfy excision for
extensions of nuclear H-unital Frechet algebras and use this to compute them
for the algebra of Whitney functions on an arbitrary closed subset of a smooth
manifold. Using a similar excision result for periodic cyclic homology, we also
compute the periodic cyclic homology of algebras of smooth functions and
Whitney functions on closed subsets of smooth manifolds.
