[jenkins] How to stop an unstoppable zombie job on Jenkins without restarting the server?

Alexandru Bantiuc's answer worked well for me to stop the build, but my executors were still showing up as busy. I was able clear the busy executor status using the following

server_name_pattern = /your-servers-[1-5]/
jenkins.model.Jenkins.instance.getComputers().each { computer ->
  if (computer.getName().find(server_name_pattern)) {
    println computer.getName()
    execList = computer.getExecutors()      
    for( exec in execList ) {
      busyState = exec.isBusy() ? ' busy' : ' idle'
      println '--' + exec.getDisplayName() + busyState
      if (exec.isBusy()) {
        exec.interrupt()
      }
    }
  }
}