In pure C++ you cannot since C++ doesn't even have the concept of a console. You could essentially be printing to anything(file, printer, dashboard) or even redirecting to another program etc.
It therefore depends on the OS or relies on you using a Library such as ncurses
In windows, for example, you can do the following
#include <stdlib.h>
int main(int argc, char* argv[])
{
system("cls");
return 0;
}