You can set it up for channel tracking in your adsense account - so it will track by the url of your sites.

Google Analytics

AdSense reports in Analytics - Analytics Help

When you create an ad at your Google Adsense account management area, you have the option of adding a "channel", which is any name/identification you want to create for a group of ads.

Best practice is to have different channels not only for different sites, but also for different ad placements.

I'm a bit lazy, so I setup only 1 channel for each site or sometimes one for each niche. But that leaves you blind as to which site is getting most clicks and deserves more of your time X sites where people are more aware of the ads and don't click it so much (like tech sites, maybe). Or simply which page is getting cheaper CPC and which is getting higher CPC, so you can investigate the keywords you are using. You might find out some ad placements gets all clicks and others almost none, so you might need to change the later to increase your revenue.