Rsync - delete extra files in Destination without synchronising directories

I have a script that synchronises a directory to a DR server, but to improve the time, I actually use rsync to transfer files *[123] in one batch and also
*[456] in another batch - both batches run from the same script and run in the background.

My problem is that there isn't much space on the Destination, so I would like to start by deleting any files on there that don't exist on the Source.

Is there any way to delete files on the Destination that don't exist on the Source only i.e. without synchronising the files?

Thanks in advance

I doubt rsync can just delete on the target without any sync.
Though there is a --delete-before option that might give you the needed place before it copies.