An apparatus is described that includes a plurality of processors, a plurality of cache slices and respective cache agents. Each of the cache agents have a buffer to store requests from the processors. The apparatus also includes a network between the processors and the cache slices to carry traffic of transactions that invoke the processors and/or said cache agents. The apparatus also includes communication resources between the processors and the cache agents reserved to transport one or more warnings from one or more of the cache agents to the processors that the one or more cache agents' respective buffers have reached a storage capacity threshold.