A data processing apparatus and method are provided for performing power management. The data processing apparatus has a plurality of domains in which devices of the data processing apparatus can operate, and comprises at least one master device for performing operations and at least one slave device for use by such master devices when performing those operations. Each master device is arranged to issue a domain ID signal identifying the domain in which that master device is currently operating. Further, power control logic is provided for determining, based on the domain ID signal issued by the various master devices, whether any portion of a slave device is not currently useable, and if so to cause any such portion to enter a power saving state. This provides a particularly efficient technique for power management in such a data processing apparatus.