A processor is disclosed. The processor includes a decoder to decode instructions and a circuit, in response to a decoded instruction, detects an incoming write back or write through streaming store instruction that misses a cache and allocates a buffer in write combining mode. The circuit, in response to a second decoded instruction, detects either an uncacheable speculative write combining store instruction or a second write back streaming store or write through streaming store instruction that hits the buffer and merges the second decoded instruction with the buffer.