Best is to investigate the ContentType Hub, a SiteCollection for storing (besides ContentTypes) any content you want to share
With JSLink you can reference files in any other Site Collection with a absolute URL, just remember the User needs read access
On Office365 you can reference files from any location
And.. On Prem... SharePoint runs on your IIS server, so you can move your scripts outside of SharePoint onto another IIS WebSite instance eg. https://scripts.[yourdomain].com
If you don't have a content type hub provisioned or available, another option is to utilize a Site Assets library (or Style Library) in a site collection everyone has access to. This could be your root site collection or your search site collection.
You could create your own script center site collection where you (and others) could store scripts usable by everyone.
The key aspect, as Danny mentions, is storing it in a library that everyone has read access to.