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]