How to deal with stale data in the client mongo database?

Perhaps strange query. Let me explain.
I am building a Meteor app which is driven by an external topic map. Those topics can change over time, some rapidly, some not so rapidly. If a user is working with a topic sequestered locally, and it stays there for, well, forever, eventually, the topic (in mongo) will go stale.
I looked at removing mongo, but that’s turning into a nightmare – running without mongo seems rather complex.
At the same time, removing a topic once it’s been viewed, forcing a refresh, seems like a terrible hack.
Please note: this is not a remote Mongo database – there have been questions similar to mine, but involving remote Mongo.

I would greatly appreciate any thoughts on this issue.
Many thanks in advance.

The only ways I can think of are these:

  1. Have the external server ping yours whenever there are updates, like web hooks.
  2. Refresh each topic from the remote every time it is used by a client.
  3. Refresh each topic at time intervals using something like percolate:synced-cron.