Abstract: A data processing apparatus and method has a plurality of processing units, at least one of which is configured to be switchable between an active power state and a dormant power state and the units share a memory, and at least one local storage unit is configured to store a local copy of a data item stored in the memory for access by an associated processing unit. A snoop control unit is monitors memory access requests and when one is issued, if the control unit has an indication that a local storage unit belonging to another dormant processing unit has a local copy of that data storage item and a cache coherency protocol required that the local copy of the requested data item associated with the other processing unit be invalidated, the control unit stores a marker indicating that that other local copy should later be invalidated.

Abstract: A data processing apparatus and method are provided for handling memory access requests to shared memory. The data processing apparatus has a plurality of processing units, at least one of which is configured to be switchable between an active power state and a dormant power state. The processing units share a memory, and at least one local storage unit is configured to store a local copy of a data item stored in the memory for access by an associated processing unit. A snoop control unit is configured to monitor memory access requests issued by the processing units and to store in the snoop control unit indications of local copies of data items stored in each local storage unit.