diff --git a/plugins/scenes/opengl/lanczosfilter.cpp b/plugins/scenes/opengl/lanczosfilter.cpp
--- a/plugins/scenes/opengl/lanczosfilter.cpp
+++ b/plugins/scenes/opengl/lanczosfilter.cpp
@@ -394,18 +394,10 @@
         delete m_offscreenTex;
         m_offscreenTarget = nullptr;
         m_offscreenTex = nullptr;
-        foreach (X11Client *c, Workspace::self()->clientList()) {
-            discardCacheTexture(c->effectWindow());
-        }
-        foreach (X11Client *c, Workspace::self()->desktopList()) {
-            discardCacheTexture(c->effectWindow());
-        }
-        foreach (Unmanaged *u, Workspace::self()->unmanagedList()) {
-            discardCacheTexture(u->effectWindow());
-        }
-        foreach (Deleted *d, Workspace::self()->deletedList()) {
-            discardCacheTexture(d->effectWindow());
-        }
+
+        workspace()->forEachToplevel([this](Toplevel *toplevel) {
+            discardCacheTexture(toplevel->effectWindow());
+        });
     }
 }
 
diff --git a/workspace.h b/workspace.h
--- a/workspace.h
+++ b/workspace.h
@@ -133,6 +133,7 @@
     Unmanaged *findUnmanaged(xcb_window_t w) const;
     void forEachUnmanaged(std::function<void (Unmanaged*)> func);
     Toplevel *findToplevel(std::function<bool (const Toplevel*)> func) const;
+    void forEachToplevel(std::function<void (Toplevel *)> func);
     /**
      * @brief Finds a Toplevel for the internal window @p w.
      *
diff --git a/workspace.cpp b/workspace.cpp
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -1720,6 +1720,15 @@
     return nullptr;
 }
 
+void Workspace::forEachToplevel(std::function<void (Toplevel *)> func)
+{
+    std::for_each(m_allClients.constBegin(), m_allClients.constEnd(), func);
+    std::for_each(desktops.constBegin(), desktops.constEnd(), func);
+    std::for_each(deleted.constBegin(), deleted.constEnd(), func);
+    std::for_each(unmanaged.constBegin(), unmanaged.constEnd(), func);
+    std::for_each(m_internalClients.constBegin(), m_internalClients.constEnd(), func);
+}
+
 bool Workspace::hasClient(const AbstractClient *c)
 {
     if (auto cc = dynamic_cast<const X11Client *>(c)) {