1. In a clustered data processing system where a first computer system includes an in-memory object and a second computer system includes a replica state of the in-memory object, a system for replicating a current state of the in-memory object comprising: a previously replicated state of the in-memory object maintained in the first computer system; difference logic for determining difference values between the current state and the previously replicated state; and communication logic for transmitting the difference values to the second computer system to modify the replica state with the difference values.