about isOverrided at C#

What should I do to distinguish it whether a derived class implements overriding of a method?

class BaseClass
    {
        public virtual void targetMethod() { return; }
    }

class DerivedClass:BaseClass
    {
        public bool isOverrideTargetMethod()
        {
            //Here, I wants to judge whether DerivedClass is overrided targetMethod.
        }
        public override void targetMethod()
        {
            base.targetMethod();
        }
    }