How do I use a site workflow to call a library workflow?

Using SharePoint 2010 and Nintex Workflow 2010

I have an SOP Document library with a CheckRevisionDate workflow, set to run manually.

I have created a site workflow that loops thru each item in the SOP Document Library, and I want to call the CheckRevisionDate workflow on each item from the Site Workflow.

What workflow part do I use and how do I configure it to make the library wrokflow start?

I am doing this so I can use the Schedule Site Workflow to do the periodic checks.