I have syncthing installed in 5 machines. One of the them is the master one in the sense that all the other connect to it, but not amongst each other. So, the master machine is a hub. Once a file is changed in any of the other machines, it is first replicated on the master machine and from there to the others.
Now, sync last last update (1.3.1), the master machine broadcasts a “version.txt” file each 5 minutes.