For the cleaning of dedicated equipment in a facility dedicated to the manufacture of a single API, is visibly clean an acceptable criterion for cleaning validation, i.e., no requirement for specific determination of the API?

Yes, visibly clean may be acceptable if we’re talking about a dedicated facility. The concern is not
cross-contamination. In a situation like that, the concern is the potential for carryover of material
left over in equipment to subsequent batches and the possibility that that material may degrade.
Instead of being focused on cleaning validation and avoidance of cross-contamination the issue
really is being on the alert for carryover of degradants.