Jenkins Multibranch Pipeline: clean workspace / delete directory when build ends

we are using Jenkins multibranch (scripted) pipeline to run multiple builds, in parallel. Each one will create a new, uniquely named directory to checkout the code and run the test. Directories are uniquely named because they contain the branch name but also a random part like "JAA2A5HUZB7TRE4OTVXU7S…".

This means that after each build X directories (X = number of parallel jobs * number of branches) stay on the Jenkins node, filling disk space.

I wonder how I could automatically delete these directories.

A simplified version of my initial pipeline looks like this

// Initialize the matrix
def matrix = [
  'foo',
  'bar',
]

// Initialize empty tasks map
def tasks = [:]

// Job status
successful = true

// Fill our tasks map from the Matrix data
for (x in matrix) {

  def job_name = x

  tasks[job_name] = {
    node('libvirt') {
        // Checkout repository first
        stage("$job_name - Checkout") {
          checkout scm
        }

        // Then build the machine
        gitlabCommitStatus('build') {
            stage("$job_name - Build") {
                  sh "./bin/build.sh ${job_name}"
            }
        }
      }
    }
  }
}


//// Pipeline ////

notifyBuild('STARTED')

// Run tasks in parallel
try {
  parallel tasks
} catch(e) {
  throw e
} finally {
  if (successful) {
    notifyBuild('SUCCESS')
  } else {
    notifyBuild('FAILED')
  }
}

// Methods
def notifyBuild(String buildStatus = 'STARTED') {
   // used to send formatted e-mails 
}

I first added deleteDir() like this

} finally {
  if (successful) {
    notifyBuild('SUCCESS')
  } else {
    notifyBuild('FAILED')
  }
  node('libvirt') {
    deleteDir()
  }
}

it raises an error and makes the build fail.

I then added a cleanWs() like this

} finally {
  if (successful) {
    notifyBuild('SUCCESS')
  } else {
    notifyBuild('FAILED')
  }
  node('libvirt') {
    cleanWs()
  }
}

The output is

Running on node in /srv/jenkins/workspace/pipeline-deletedir-DRD7EKBEMMWJQZW6KKMQVVBTJTPTKLRAE2ITDK7V7IB5PTFXZUZA
[Pipeline] {
[Pipeline] step
[WS-CLEANUP] Deleting project workspace...[WS-CLEANUP] done
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS

but the directory /srv/jenkins/workspace/pipeline-deletedir-DRD7EKBEMMWJQZW6KKMQVVBTJTPTKLRAE2ITDK7V7IB5PTFXZUZA still exists.

I'm looking for any solution to adapt this scripted pipeline (and for declarative pipeline if you know how) to be able to delete all directories created by the build.