Cache memory system for selectively storing directory information for a higher level cache in portions of a lower level cache

A cache memory system for use with an external cache system comprising at least one data array includes one or more cache data arrays and corresponding cache directory arrays. The cache memory system operates in one of at least two modes of operation. In a first mode of operation, the cache data arrays store data relating to directory information stored in the corresponding cache directory arrays. In a second mode of operation, at least a portion of the cache data arrays stores directory information corresponding to the at least one data array of the external cache system.