Add a WorkspaceListener extension point

core/src/main/java/hudson/model/AbstractProject.java

@@ -1761,6 +1761,9 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
         FilePath ws = b!=null ? b.getWorkspace() : null;
         if (ws!=null && getScm().processWorkspaceBeforeDeletion(this, ws, b.getBuiltOn())) {
             ws.deleteRecursive();
+            for (WorkspaceListener wl : WorkspaceListener.all()) {
+                wl.afterDelete(this);
+            }
             return new HttpRedirect(".");
         } else {
             // If we get here, that means the SCM blocked the workspace deletion.

core/src/main/java/hudson/model/WorkspaceListener.java

+package hudson.model;
+
+import hudson.ExtensionList;
+import hudson.ExtensionPoint;
+
+public abstract class WorkspaceListener implements ExtensionPoint {
+    
+    /**
+     * Called after a workspace is deleted successfully.
+     * @param project
+     */
+    public void afterDelete(AbstractProject project) {
+        
+    }
+    
+    /**
+     * All registered {@link WorkspaceListener}s.
+     */
+    public static ExtensionList<WorkspaceListener> all() {
+        return Hudson.getInstance().getExtensionList(WorkspaceListener.class);
+    }
+
+}