How to clean dirty test pins in bulk?
Test probes are typically a two part assembly. One part is the pogo pin itself and the other is a socket that the pogo pin slides into. The socket part is mounted into the base plate part of the test fixture. Test fixtures are designed this way so that broken or faulty pins can be easily replaced without having to disassemble the whole fixture. 

Cleaning contacts can be done by removing them from the fixture. An ultrasonic cleaning unit can be a good way to clean the contacts without physical damage to them. After cleaning you will have to consult with the pogo pin manufacturer to determine if any lubrication is necessary. (It has been my experience that the platings used on pogo pins and their spring loaded plungers so not inherently require any lubrication).

Typical ultrasonic cleaning unit: