1. An apparatus for monitoring the processing of coherence event signals in a multiprocessor system, said multiprocessor system having a plurality of processors, each processor having a dedicated memory storage device, said processors generating coherence events broadcast to other processors, each said processor having an associated snoop unit comprising: a plurality of multiple coherence ports for receiving said coherence event signals from each processor in said multiprocessor system; a coherence traffic processing unit for processing said coherence event signals and forwarding said processed coherence event signals to said processor to which said snoop unit is attached; a coherence port to processor unit for receiving and transmitting said forwarded coherence event signals from said coherence traffic processing unit to said processor; one or more mode registers programmed to receive one or more bits values that, when set, initiate performing a single-step operation in said multiprocessor system; and one or more single-step registers programmed to receive one or more bit values that, when set, initiate processing of a single coherence event signal in a single-step operation mode.