Where does SYSTIMESTAMP come from in multi-server Oracle RAC environment?

Where does SYSTIMESTAMP come from in multi-server Oracle RAC environment? I'm hoping that the SYSTIMESTAMP derives from a common location (master node?) as opposed to the server that is currently servicing the request. Additional Detail: -------------------- We are using a timestamp to ensure that entries in a log table are recorded sequentially. Say, for example, we have two nodes in our RAC and they are 1 second off. Our app server inserts two log entries within, say, 0.03 seconds of each other. The first insert is serviced by Node1 and the second by Node2. If there is one second difference between the two nodes, the timestamp could potentially show the log entries occurring in the wrong order! (I would just use a sequence, but our sequences are cached for performance reasons... )