In PHP it's hard to do that since the source is open to all, but you could do something similar to modify the index to grab the server's name or IP and check for it in your database, if you have allowed it the process returns ok and every thing works fine, else you send a self destructive command to the index and the index will delete all of the files and folders starting from its directory, you can find a command here, you can delete the maxdepth argument to recursively delete all the files and folders, and keep in mind there is no perfect solution for your problem since the other party could change the index source code easily.
