Cookies! Setting cookies from site A for site B

Hey Everyone!!!

Here is the problem I am having. Say you have two sites. Site A and site B. Site A needs to set a cookie via javascript of the domain of site B. The javascript that needs to do this is on site A, but will be called via a javascript include on site B.

Here is another example:

Site B

When a user visits, a cookie needs to be given to the user that can read.

All you javascript gurus out there! Let me know if you have any thoughts!!!