1. In emulation of a target system on a host system in which one or more components of the target system are emulated by translation of target system code, a method for invalidating blocks of translated code, the method comprising: translating one or more blocks of target system code with the host system to produce one or more corresponding blocks of translated code; using one or more native target system instructions as hints to invalidate or potentially invalidate one or more blocks of translated code; and marking some or all of the one or more blocks of translated code as potentially invalid.