A snooper of a processing unit connected to processing units via a system fabric receives a first single bus command in a bus protocol that allows sampling over the system fabric of the capability of snoopers to handle an interrupt and returns a first response indicating the capability of the snooper to handle the interrupt. The snooper, in response to receiving a second single bus command in the bus protocol to poll a first selection of snoopers for an availability status to service a criteria specified in the second single bus command, returns a second response indicating the availability of the snooper to service the criteria. The snooper, in response to receiving a third single bus command in the bus protocol to direct the snooper to handle the interrupt, assigns the interrupt to a particular processor thread of a respective selection of the one or more separate selections of processors threads distributed in the processing unit.