Seeing strange behavior while studying http://goo.gl/id2JNj ... The following seems to reset (i.e., to Clear) the definition of holdAsgts ClearAll[holdAsgts, a, b];
SetAttributes[holdAsgts, HoldAll];
holdAsgts[(set : Set | SetDelayed)[L_, R_]] :=
{L, R}; holdAsgts[a := 42, b];