No, you don't have to actually file before a garnishment will reflect in their system.
For non-IRS debts, you can contact the Bureau of the Fiscal Service (BFS) directly at (800) 304-3107 to find out if there is a pending offset of your refund and for how much. In most cases, this service is pretty accurate, so if they don't report an offset on file for you, it is most likely correct.