1. An apparatus for monitoring 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 coherence protocol 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 coherence protocol unit is attached; a coherence port 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 bit 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, wherein said coherence port unit further comprises: a state machine coupled to said one or more mode registers and said one or more single-step registers for determining the status of said one or more mode registers and said one or more single-step registers; and, a data path coupled to said coherence traffic processing unit and said processor, wherein said coherence event signals are processed by said data path under control of said state machine.