As of today, shops will have a single domain. The default domain is .com so no action is required if you want your shop to remain on .com. If you want to update your shop domain from .com to one of the other domain options, you can do so in your Shop Profile page. Other domain options currently include: .ca, .co.uk, .com.au, .de, .fr, and .es.
www.cafepress.com/shopidexample <– .com is the default domain
If you want the shop to be on .fr, you will need to select .fr on your Shop Profile page so your shop domain becomes www.cafepress.fr/shopidexample