Finally released the Nexus Guide by Scrum.org to scale agile in the organizations, to download the guide click here: https://www.scrum.org/Resources/The-Nexus-Guide . Moreover, from Scrum.org one can do the Nexus Open test, suggested to do after studying the Nexus Guide.
Nexus is a framework consisting of roles, events, artifacts, and techniques that bind and weave together the work of approximately three to nine Scrum Teams working on a single Product Backlog to build an Integrated Increment that meets a goal.