Google analytics gives us the ability to modify tracked through filters. The following screenshot tells us how to modify Request URI and add the hostname to it:

About cross domain tracking: https://support.google.com/analytics/answer/1033876

To setup cross domain tracking from either Google Analytics or Google Tag Manager: https://support.google.com/analytics/answer/1034342

To setup Analytic Reports to include the domain name: https://support.google.com/analytics/answer/1034342#Next