1. A system comprising: an agent configured to initiate a transaction addressing a first cache block; a cache coupled to receive the transaction, the cache including a plurality of cache block storage locations for storing cache blocks; wherein the agent is configured to transmit a cache allocate indication in the transaction, wherein the cache allocate indication indicates whether or not the cache is to allocate one of the plurality of cache block storage locations to store the first cache block if the transaction is a miss in the cache; and wherein the cache, if the transaction is a miss, is configured to selectively allocate one of the plurality of cache block storage locations to store the first cache block responsive to the cache allocate indication.