can rawbytestring cleared from memory ?

[Madammar]

i have tried mostly all way to make it zero memory but i can see the plain text in memory

here is my code

Code:

var
password: ISecureString;
rawstring : rawbytestring;
begin
password:= NewSecureString('sometext');
rawstring :=UTF8Encode((password.Data);

if rawstring <> '' then
begin
FillChar(PAnsiChar(rawstring)^, Length(rawstring), 0);
end;

end;