The Collaborative International Dictionary of English v.0.48:

Invalidation \In*val`i*da"tion\, n.
   The act of inavlidating, or the state of being invalidated.
   [1913 Webster]

         So many invalidations of their right.    --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

invalidation
    n 1: (law) a formal termination (of a relationship or a judicial
         proceeding etc) [syn: annulment, invalidation]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "invalidation":
   abolishment, abolition, abrogation, annulment, cancel, canceling,
   cancellation, cassation, counterbalancing, countermand,
   counterorder, defeasance, disconfirmation, disproof, disproval,
   disproving, explosion, expose, exposure, frustration, negation,
   neutralization, nullification, offsetting, recall, recantation,
   redargution, reductio ad absurdum, renege, repeal, rescinding,
   rescindment, rescission, retraction, reversal, revocation, revoke,
   revokement, setting aside, suspension, thwarting, undoing,
   vacation, vacatur, vitiation, voidance, voiding, waiver, waiving,
   withdrawal, write-off