An apparatus has processing circuitry (18), and memory access circuitry (35) to control access to a memory system based on memory attribute data identifying each memory region as one of a plurality of region types. A speculation-restricted region type is supported, for which: at least when a first read request is non-speculatively issued to a region of the speculation-restricted type, a subsequent read request is permitted to be serviced using data obtained in response to the first read request; and for a speculatively issued read request to the region of the speculation-restricted type, at least when caching the read data would require allocation of a new entry in the cache, at least one response action, which is permitted for non-speculatively issued read requests specifying a target memory region of the speculation-restricted region type, may be prohibited from being performed before the first read request has been resolved as correct.