1. A method of maintaining cache coherency in a multiprocessor computer system having a plurality of processing units, each processing unit having at least one cache, each of the caches having a plurality of cache lines, and each of the cache lines being divided into a plurality of sectors, comprising the steps of: issuing a request from a first cache to retrieve an entire cache line; and sourcing only a first sector of the cache line from a second cache to the first cache, in response to said issuing step.