The way Cloudflare works is it will cache resources only after they are requested, and for a TTL set either at the origin server or by an Egde Cahe TTL setting, whichever is larger. Assets that are infrequently requested, though, may me purged before their TTL expiration.
So if a visitor from somewhere requests a page and subsequent files, and the visitor is routed to the CDG (Paris) data center, these files will be cached at CDG for their respective TTL. When another visitor is routed to IAD, these files will be cached at IAD. And so on, and so forth.
Any file requested from a data center where the file hasn’t been cached will be fetched from the origin server, and cached for the next visitor routed to this data center.
Cloudflare offers a paid service called Argo that will make it fetch uncached files from the nearest data center where the file is already cached, instead of going back to the origin. This service is billed on usage and is available in all plans.