Processor-to-processor (P-P) and/or broadcast proxies may be designated in a microprocessor matrix comprising a plurality of mesh-interconnected matrix processors when default processor-to-processor or broadcast routing algorithms used by data switches within the matrix to route messages would not deliver the messages to all intended recipients. The broadcast proxies broadcast messages within individual non-overlapping broadcast domains of the matrix. P-to-P and broadcast proxies may be designated as part of a boot-time testing/initialization sequence. Improving system fault tolerance allows improving semiconductor processing yields, which may be of particular significance in relatively large integrated circuits including large numbers of relatively-complex matrix processors.