1. A data processing apparatus comprising: processing circuitry configured to perform data processing; a memory attribute unit comprising a plurality of storage regions, each storage region configured to store attribute data for controlling access to a corresponding memory address range by the processing circuitry; and wherein in response to a target memory address, the processing circuitry is configured to perform a region identifying operation to determine which of the plurality of storage regions of the memory attribute unit is a matching storage region for which the corresponding memory address range includes said target memory address, and to output a region identifying value identifying which of said plurality of storage regions of the memory attribute unit is said matching storage region for the target memory address, wherein the target memory address is a physical address and the region identifying value is made available to at least some software executed by the data processing apparatus.