Like @gotgenes pointed out with Jenkins Version. 2.74, the below works, not sure since when, maybe if some one can edit and add the version above
cleanWs()
With, Jenkins Version 2.16 and the Workspace Cleanup Plugin, that I have, I use
step([$class: 'WsCleanup'])
to delete the workspace.
You can view it by going to
JENKINS_URL/job/<any Pipeline project>/pipeline-syntax
Then selecting “step: General Build Step” from Sample step and then selecting “Delete workspace when build is done” from Build step