Linda,
Easa Part-FCL says:
For a multi-engine IR(A), the skill test shall be taken in a multi-engine aeroplane. For a single-engine IR(A), the skill test shall be taken in a single-engine aeroplane.
Nothing is said about the revalidation wether it has to be done single or multi engine. But here in Holland they do interpret the revalidation as having to be done on a multi if you want IR/ME.