Credentials plugin uses the term "global" for two very different concepts:

Global scope

This credential is available to the object on which the credential is associated and all objects that are children of that object. Typically you would use global-scoped credentials for things that are needed by jobs.

Global credentials domain

All credentials that are not bound to a specific domain

This should be changed by renaming one of them to prevent user confusion.

Suggestions: Unbound domain, inheriting scope