1. A method of handling interrupts in a data processing system, the method comprising: receiving, at an interrupt presentation controller (IPC), an event notification message (ENM), wherein the ENM specifies a level, an event target number, and a number of bits to ignore; determining, by the IPC, a group of virtual processor threads that may be potentially interrupted based on the event target number, the number of bits to ignore, and a process identifier (ID) when the level specified in the ENM corresponds to a user level, wherein the event target number identifies a specific virtual processor thread and the number of bits to ignore identifies the number of lower-order bits to ignore with respect to the specific virtual processor thread when determining the group of virtual processor threads that may be potentially interrupted; and selecting a single virtual processor thread from the group of virtual processor threads to service the interrupt.