Find the name of the invoked method of a Funz delegate

I have a simple invoker where, in order to be able to put some caching logic, I need to know the name of the invoked method of an object that is a parameter of a Func delegate.

 class Program
        {
            static void Main(string[] args)
            {
                var proxy = new Proxy();        
                Invoker.invoke(proxy, p => p.formatSomething("Dumb test"));       
            }
        }

        public class Proxy
        {
            public string formatSomething(string input){

                return String.Format("-===={0}====-", input);
            }
        }


        public static class Invoker
        {        
            public static void invoke(Proxy proxy, Func<Proxy,string> online){                       

             //Some caching logic that require the name of the method 
             //invoked on the proxy (in this specific case "formatSomething")    
             var methodName = ??; 
             SomeCacheLogic(methodName);       
             var output = online(proxy);

            }

        }        

Except adding an error prone string parameter where I could specify the name of the called method to the Invoker, do you know any other better way to inspect and get the methodName the Invoker needs?