The Copy with Scaffolding XML feature can only copy pages within the same space.
To copy a page with Scaffolding data to another space will require a workaround by entering the following URL:
Please replace the following:
<BASE-URL> = Your Confluence base URL
<PAGE-ID-COPY> = The page ID that you want to copy
<PARENT-PAGE> = The page ID of the targeted parent page
<SPACEKEY> = The space key of the targeted space