https://support.google.com/analytics/answer/1033162?hl=en-GB
Note that this doesn't apply retrospectively to your data, so it will only apply to data collected after you make a change. You might want to create an advanced segment which filters out these domains, or only includes the ones that you want.
https://www.google.co.uk/intl/en/analytics/features/advanced...
https://support.google.com/analytics/answer/1033162?hl=en-GB
Note that this doesn't apply retrospectively to your data, so it will only apply to data collected after you make a change. You might want to create an advanced segment which filters out these domains, or only includes the ones that you want.
https://www.google.co.uk/intl/en/analytics/features/advanced...