Verify that a website is hosted only on an allowed domain address

[NeoMarine]

I'm curious, how can I basically set up something like:

 

if (HTTP_HOST!="http://www.alloweddomain.com"){

die("You're using an illegal copy of this script.");

}

 

To help protect my scripts. I realize I would need to hide that section of code and even obfuscate it, which I probably can do, but I'm trying to make a "kill switch" for anyone attempting to pirate my scripts.