Unless a single user cross posted the same question [*(different discussion)*](https://meta.stackexchange.com/q/64068/217279) there is no such thing a cross site duplicate. They are either in scope or out of scope, if they are inscope they should be open. 

> You can't assume that all users will be on all sites. Each site has to stand on its own merits and you have to treat each site as a separate community.
>
> If a question is inappropriate on one site, users now have alternate places to go with it. It's a nice convenience if moderators choose to transfer it for them. If it turns out to be a duplicate, let the other community handle it with the means already in place. If the first moderator happens to spot it as a cross-site duplicate, it can simply be closed and the original poster can decide how to rework the question if they want to try it on another site.
>
> In the edge case where the question is appropriate on more than one site, leave it on both sites and let the users of each community benefit from the information. [Source Robert Cartaino at Meta.SE](https://meta.stackexchange.com/a/4713/217279)