Hi Brian. There is a workflow action called "Copy to SharePoint" which allows you to select and copy to a Document Library on another site. I have just been playing around with this myself and seems to do what you're looking for.

Hi, I cannot find copy to SharePoint action in my Nintex workflow. Any ideas where it could be? thanks. I am using evaluation version of Nintex.

Hi Brian,

Make sure this action is allowed in your environment. To check site and site collection level you should look at Site settings->Nintex workflow->Manage allowed actions and also this can be restricted from farm level which you need to look at Central administration -> Nintex workflow management -> manage allowed actions. Please make sure in all places this action is selected.

Not sure.. tried Copy to Sharepoint for transferring Document Sets, but it does copy seperately both Document Set and files within the set..