Is it possible to share consent across different main domains?

Yes, you can share consent across different main domains by using the "Group Cookies" functionality.

This allows the consent to be stored on a subdomain that you own and delegate to us, such as privacy.your-domain.com. 

The consents will be shared only between the domains that have this feature activated with the same specific subdomain. 

This enables private consent among all your sites without third-party exposure.  For more details, such as limits & obligations, please refer to the Didomi documentation here.