An apparatus, system, and method are disclosed for externally invalidating an uncertain cache line. In one embodiment, a monitor module monitors a processor module bus. A detection module detects a processor module evicting a cache line from a cache module. The cache line may be in an uncertain state. An invalidation module invalidates the cache line with an invalidation command directed to the processor module. In one embodiment, an update module updates a cache directory external to the processor module. The apparatus, system, and method increase memory and processor bandwidth by eliminating the need to snoop the processor module bus for evicted cache lines.