I want to allow a script to run only if it is physically inside a specific domain.

Why? As a security measure, this won't be effective. But to answer your question: www.univie.ac.at resolves to 131.130.70.8, and a Whois lookup at http://www.ripe.net/ shows that "Vienna University Computer Center" owns the entire block of IP addresses 131.130.0.0 to 131.130.255.255. So you could check whether an IP address is in that range. But IPs are easily spoofed, so again, as a security measure it isn't very effective. But it might be fine if you just wanted to have a guess at the location of the machine.