When you delete jobs in Jenkins, the corresponding workspaces in the build slaves won't be deleted automatically. This Jenkins script will go to each slave and check if the jobs are already deleted in Jenkins master and delete the workspace.

cleanupUnusedWorkspaceInSlaves.groovy

import com.cloudbees.hudson.plugins.folder.Folder
import hudson.FilePath
import jenkins.model.Jenkins

def boolean isFolder(String name) {
    def item = Jenkins.instance.getItemByFullName(name)
    return item instanceof Folder
}

def deleteUnusedWorkspace(FilePath root, String path) {
    root.list().each { child ->
        String fullName = path + child.name
        if (isFolder(fullName)) {
            deleteUnusedWorkspace(root.child(child.name), "$fullName/")
        } else {
            if (Jenkins.instance.getItemByFullName(fullName) == null) {
                println "Deleting: $fullName "
                child.deleteRecursive()
            }
        }
    }
}

for (node in Jenkins.instance.nodes) {
    println "Processing $node.displayName"
    def workspaceRoot = node.rootPath.child("workspace");
    deleteUnusedWorkspace(workspaceRoot, "")
}

Sorry I missed all previous comments. I haven't used Jenkins for a while. You can comment on the code that deletes the workspace and see what "println "Processing $node.displayName"" would print out before you proceed.

Hi @ceilfors
I did the same and I see it prints the slave node name. Anyways, I would read some Jenkins scripting docs to find out about the master.
Thank you again!