security - Check for a domain -

How can I test whether the request for the API is coming from the right registered domain?

You can not do

You can check the IP from the server, but 1 server can control the $ n domain.

I have tested with Google: Token my Google Map API key, That's just giving me ping and receiving domain IP server; But the API key is valid from every domain on that server ... while changing the server (second with separate IP) the same API key returns an error