cookie sharing

Is there anything in P3P that prevents the sharing of the same cookie across
subdomains?  example:  sales.acme.com and marketing.acme.com use the same
cookie and policy.
 
I have searched through a lot of the documentation and cannot find anything,
yet I have been told by a number of other developers that cookie sharing is
(or will be) prohibited by P3P.
 
Any help on this is greatly appreciated.