Positioning a tikz scope relative to another tikz scope

Here is a solution using local bounding box to get the bounding box of the first scope and using shift to define the origin of the second scope:

\documentclass[tikz]{standalone}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
  \begin{scope}[local bounding box=scope1]
    \draw (2,2) rectangle (3,4);
  \end{scope}
  \begin{scope}[shift={($(scope1.east)+(1cm,0)$)}]
    \draw (0,0) rectangle (2,1);
  \end{scope}
\end{tikzpicture}
\end{document}

Edit: the answer below is here for reference but note that nesting tikzpictures is discouraged due to some subtle side-effects that this may cause. In most cases, to build a "modular" picture you can use the pic action documented in Chapter 18 of the documentation. In simpler cases like the one in the question, a combination of shift and fit usually suffices.

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If you need to keep the two scopes separated and wish to use them as "modules" I would suggest you use two nodes with nested tikzpictures as in

\begin{tikzpicture}
    \node(scope1){
        \begin{tikzpicture}
           \draw (1,2) rectangle (3,4);
        \end{tikzpicture}
    };
    \node[at={($(scope1.east)+(1cm,0)$)},anchor=west] (scope2){
        \begin{tikzpicture}
             \draw (5,6) rectangle (7,8);
        \end{tikzpicture}
    };
\end{tikzpicture}