Question about setting cookies for include/exclude filters on Google Analytics

1. I want to set a cookie with the name "gatracking" for all members of my site and set up an exclude filter in GA that excludes anyone who has the "gatracking" cookie from tra开发者_如何学Goffic on the homepage. If another site is coincidentally using a cookie with the same name, how would the GA exclude filter treat that? Will the filter only consider cookies set on the specific domain it is tracking, or just look for any cookie with the name "gatracking" in my saved cookies?

2. If the "gatracking" cookie is being set on app.mydomain.com, can it be set to include www.mydomain.com?

Google has more details on cross domain tracking. Including cross subdomain. Take a look at their docs. It could be helpful.

http://code.google.com/apis/analytics/docs/tracking/gaTrackingSite.html