The dbcc checkdb and dbcc checktable commands check the page chains for a table, building the look-ahead set in the same way as other sequential scans.
If the table being checked has nonclustered indexes, they are scanned recursively, starting at the root page and following all pointers to the data pages. When checking the pointers from the leaf pages to the data pages, the dbcc commands use asynchronous prefetch in a way that is similar to nonclustered index scans. When a leaf-level index page is accessed, the look-ahead set is built from the page IDs of all the pages referenced on the leaf-level index page.
