How to create a lightweight domain access alternative in Drupal 7
Out of the box drupal 7 installs are domain agnostic (don't save absolute urls in content or as paths). Assuming you haven't got any custom server directives or alternate domain with a need for a different relative url, you could try either:

A) Create a separate content type, if content managers know up front what content will need to be visible. 

B) But if they don't know up front (and since you can't easily convert a node from one type to another), you could try using a taxonomy field to tag content for visibility. Then use taxonomy access lite module (https://www.drupal.org/project/tac_lite) to grant access to nodes tagged with a specific term to anonymous users.