Speculative cache storage region

An apparatus (2) comprises processing circuitry (4) to perform speculative execution of instructions; a main cache storage region (30); a speculative cache storage region (32); and cache control circuitry (34) to allocate an entry, for which allocation is caused by a speculative memory access triggered by the processing circuitry, to the speculative cache storage region instead of the main cache storage region while the speculative memory access remains speculative. This can help protect against potential security attacks which exploit cache timing side-channels to gain information about allocations into the cache caused by speculative memory accesses.