Partition identifier space selection

Processing circuitry processes instructions in one of at least three domains each associated with a corresponding physical address space, and issues a memory access request to a memory system, the memory access request comprising a partition identifier (selected based on programmable partition identifier selection information associated with a current software execution environment which caused the memory access request to be issued) and a multi-bit partition identifier space indicator indicating a selected partition identifier space (selected from among at least three partition identifier spaces based on a current domain of the processing circuitry). The selected partition identifier space and partition identifier together represent information for selecting, at a memory system component, parameters for controlling allocation of resources for handling the memory access request or managing contention for said resources, or for selecting whether performance monitoring data is updated in response to the memory access request.