If you are able to quench the parts while a little hot, when the braze alloy has solidified but the parts have not cooled down, the flux will typically just break off by itself because of the quench.
Typically flux will cake the parts. However, depending on what metal is used as the base metal, if you are able to quench the metal parts while the parts are a little hot, when the braze alloy has solidified but the parts have not cooled down, the flux will typically just break off by itself because of the quench. You must make sure the braze alloy has solidified before you quench the part. If you are not able to quench it, you will have to employ bead blasting or a mechanical means to clean the parts. If you can’t do either, there are some chemicals available that serve as chemical cleaning solutions, although they are not fast.