Each node of a multiprocessor computer system includes a main memory, a cache memory system and logic. The main memory stores memory lines of data. A directory entry for each memory line indicates whether a copy of the corresponding memory line is stored in the cache memory system in another node. The cache memory system stores copies of memory lines and cache state information indicating whether the cached copy of each memory line is an exclusive copy. The logic of each respective node is configured to respond to a transaction request for a particular memory line and its corresponding directory entry, where the respective node is the home node of the particular memory. When the cache memory system of the home node stores an exclusive copy of the particular memory line, the logic responds to the request by sending the copy of the particular memory line retrieved from the cache memory system and a predefined null directory entry value, and thus does not retrieve the memory line and its directory entry from the main memory of the home node.