Cache Eviction not Reflected in Monitoring

I've set up the following response mapping template to initiate cache eviction on a certain dynamic cache key. It seemingly works after some testing, but is not reflected in monitoring, making me think that I've wrote the template incorrectly. If anyone can help verify the template or direct me that would be great, I am quite lost.

$util.qr($ctx.result.put("__operation", "Mutation"))
#if( $ctx.error )
  $util.error($ctx.error.message, $ctx.error.type)
#else
  #set($cachingKeys = {})
  $util.qr($cachingKeys.put("context.arguments.school", $ctx.args.input.school))
  $extensions.evictFromApiCache("Query", "announcementsBySchool", $cachingKeys)

  $util.toJson($ctx.result)
#end