And because I want to be constructive, here's how the DoubleClick redirect works. If the site has advertising features enabled, a task in analytics.js named "d

And because I want to be constructive, here's how the DoubleClick redirect works. If the site has advertising features enabled, a task in analytics.js named "displayFeaturesTask" fires after the /collect hit to Google Analytics has been sent. This task compiles a small payload of information and ships it to https://stats.g.doubleclick.net/ https://stats.g.doubleclick.net/. This payload includes, among other things, the UA ID of the Google Analytics property, and the Client ID of the user (same UA ID and Client ID that's sent with the GA hits). When you go into Analytics 360 and build those audiences, you are essentially building a dataset of Client IDs that should be included in the audience. When that data set is passed to DoubleClick, DC can then link those Client IDs to the third-party cookie written on doubleclick.net and assigned to the same Client IDs. That's how it can leverage both your GA data and its cross-site tracking network to target the audiences. As I wrote, any possible 3P cookies written on google-analytics.com are not used in this process. The request to google-analytics.com only leverages the GET/POST payload sent with the request itself.