1. A data processing system, comprising: a plurality of processing units, each processing unit comprising: notification storage circuitry configured to store a notification indicator corresponding to each processing unit which indicates whether the processing unit has an outstanding coherent memory request; and multiple request storage circuitry configured to store a multiple request indicator corresponding to each processing unit which indicates whether the processing unit has more than one outstanding request; and an interconnect network coupled between the processing units and configured to broadcast coherent memory requests from a requesting processing unit of the plurality of processing units to other processing units of the plurality of processing units.