Systems and techniques for synchronizing transactions between processing devices on an interconnection network are provided. Upon receiving a stream of posted transactions followed by a flush transaction from a source processing device connected to the interconnection network, the flush transaction is trapped before it enters the interconnecting network. Subsequently, based on monitoring for responses received from a destination processing device for transactions corresponding to the posted transactions, a flush response is generated and returned to the source processing device. The described techniques enable efficient synchronizing posted writes, posted atomics and the like over complex interconnection fabrics such that a first GPU can write data to a second GPU so that a third GPU can safely consume the data written to the second GPU.