Add explicit note on redeclaring in each application context

Closes gh-34843

spring-context/src/main/java/org/springframework/scheduling/annotation/EnableAsync.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -146,6 +146,12 @@ import org.springframework.core.Ordered;
  * compile-time weaving or load-time weaving applying the aspect to the affected classes.
  * There is no proxy involved in such a scenario; local calls will be intercepted as well.
  *
+ * <p><b>Note: {@code @EnableAsync} applies to its local application context only,
+ * allowing for selective activation at different levels.</b> Please redeclare
+ * {@code @EnableAsync} in each individual context, for example, the common root web
+ * application context and any separate {@code DispatcherServlet} application contexts,
+ * if you need to apply its behavior at multiple levels.
+ *
  * @author Chris Beams
  * @author Juergen Hoeller
  * @author Stephane Nicoll