Methods and apparatus for acknowledging and verifying the completion of data transactions over an inter-processor communication (IPC) link between two (or more) independently operable processors. In one embodiment, a host-side processor delivers payloads over the IPC link using one or more transfer descriptors (TDs) that describe the payloads. The TDs are written in a particular order to a transfer descriptor ring (TR) in a shared memory between the host and peripheral processors. The peripheral reads the TDs over the IPC link and transacts, in proper order, the data retrieved based on the TDs. To acknowledge the transaction, the peripheral processor writes completion descriptors (CDs) to a completion descriptor ring (CR). The CD may complete one or more TDs; in optimized completion schemes the CD completes all outstanding TDs up to and including the expressly completed TD.