asp.net Forms authentication across domain does not work for locally running app

Note: all the apps i am talking here are asp.net 4.0 mvc 4 app and
- server: Windows 2008, IIS v7
- local: Windows 7, IIS v7.5

we have implemented single sign on thing based on asp.net forms authentication
the idea was to share auth-cookies across domain.
see : http://msdn.microsoft.com/en-us/library/eb0zx8fc ...