1. A cache memory system for caching data comprising: a cache memory for storing a copy of a portion of data stored in a system memory; a cache load circuit capable of retrieving the portion of data from the system memory, of selecting a region of the cache memory in which to store the retrieved portion of data, and of storing a copy of the retrieved portion of data in the selected region of the cache memory; and a status memory identifying whether a region of the cache memory contains data that has been accessed from the cache memory by an external device, wherein the cache load circuit is arranged such that the region of the cache memory selected for storing the retrieved portion of data is a vacant region or a region identified as containing data that has been accessed by an external device.