Local docs cannot be queried as normal docs are. I would suggest making a separate database for them and making normal documents and just don’t do any replication.
By “local docs” do you mean regular documents created on-device, or via the “local document” API?
The “local document” API creates docs in a separate store that are not queryable. It’s a holdover from CouchDB and not used much; in CBL 2 we’ve gotten rid of that feature.
If you have documents you don’t want replicated, you can create a separate database for them and just don’t replicate that database.