The Cat6509 supports IGMP snooping which has the same functionality as the CGMP but none of the limitations. The command to enable igmp snooping is "set igmp enable" The Cat6509 MSFC supports the CGMP server feature reguired to operate CGMP on the 4006s and 2980Gs.
Here is a link to a document that has more details:
http://www.cisco.com/warp/customer/473/22.html