I have been working on rewriting a monolith into individual services during past year at work - and what we finally implemented for consistency across different databases of services was that we keep a signal queue - where whenever we encounter an inconsistency, a doc is pushed containing the info and we have a corrective service always reading from that queue and doing the necessary updates to tables. We made a heirarchy of source-of-truthness and we use that to decide what to do with inconsistent data. Though, users sometimes have to see a error messagge "We had an error and we are fixing it in few XXX time" based on current queue load - but it has been working fine mostly for us.