DMXSync man page
DMXSync — flush protocol requests between Xdmx and back-end X servers
Bool DMXSync(Display *dpy);
DMXSync() flushes all pending protocol requests between the Xdmx(1) server and each back-end X server. It is used by clients that talk directly to back-end X servers to ensure that all pending Xdmx(1) requests have reached all back-end servers and have been processed by those servers.
DMXSync() returns True unless there is a protocol error.