In a global shared memory (GSM) environment, an initiating task at a first node with a host fabric interface (HFI) uses epochs to provide reliability of transmission of packets via a network fabric to a target task. The HFI generates a packet for the initiating task addressed to the target task, and automatically inserts a current epoch of the initiating task into the packet. A copy of the current epoch is maintained by the target task, which accepts for processing only packets having the correct epoch, unless the packet is tagged for guaranteed-once delivery. When a packet delivery is accepted, the target task sends a notification to the initiating task. If the initiating task does not receive the notification of delivery for the issued packet, the initiating task updates the epoch at both the target node and the initiating node and re-transmits the packet.