Dynamic presence vector scaling in a coherency directory

In a system of multiple caching agents accessing shared cache lines, a dynamic vector scaling mechanism is achieved through the selection of a mode to grant a caching agent that requests access to a cache line. Cache line entries in a directory indicate the particular caching agents that are sharing the line of cache. Modes may include a grouping of multiple caching agents or a representation of a single caching agent. A mode may be determined for additional caching agents. The selection and determination may include determining whether to maintain or change the modes of the caching agents. The selection of the modes for the caching agents may allow the vector to assume a representation in which the caching agents are grouped in such a way as to reduce a number of invalidation requests of a cache line.