When a question is cross-posted from another StackExchange site, such as Superuser, I assume that we do not want the question duplicated on Unix and Linux. It is bad etiquette for someone to do so, and questions can be moved between sites.
When flagging a post for moderator attention, there is an "exact duplicate" option. This option requires linking to a question on U&L, and does not allow linking to another SE site. Should there be a separate flag for cross-posting?