1. A compression engine for a cache memory subsystem, the cache memory subsystem having a cache tag memory and a cache data memory, where the cache data memory is organized as a plurality of sublines, the compression engine comprising: a pointer into the cache tag memory and the cache data memory; an interface coupled to the pointer, and capable of being coupled to cache tag memory, and cache data memory, the interface capable of reading tag information and uncompressed data, and of writing modified tag information and compressed data; compression logic, the compression logic coupled to apply at least one compression algorithm to data read by the interface to generate compressed data and generate compression successful information; and tag line update circuitry for generating modified tag information according to the compression successful information and the tag information.