If you want to use the same map over again for different domains, you will have to get a different api key for each of the domains you are using it for.
If you are uploading the same pages to different domains, you will have to change the api key accordingly. On the page you have the map applied, find the map script that looks similar to this:
The key= portion stores the api key that is used. Replace that with the correct api key for each domain.