That seemed promising, but when I stop Caché, the cache.lck file is removed, and appears again when I restart the instance.
Yes, the root database name is not the same as my caché system. Caché is installed in the typical c:\intersystems\instance while these namespaces' databases are on another drive - e:\datasets. Also, we changed the underlying Windows security recently for our 2016 upgrade, so I'll have to make sure the instance's service user has access to the e:\ drive.
This is what appears in the cache.lck file: