I think that i have a possible solution, but i'm not sure if this will work and if can cause a security error.
In addition, is not a very elegant way, but can be a emergency solution.
I can get the cookie information with Javascript on the domain1.com and send via AJAX to domain2.com/controller.
In domain2.com i can set up a controller that get the cookie information and create a new cookie with the same data on domain2.com.
You think this is possible? May work safely and correctly?
Hope this can help.
Thanks