  There is a natural connection between the third homology of
$\textrm{SL}_2(A)$ and the refined Bloch group $\mathcal{RB}(A)$ of a
commutative ring $A$. In this article we investigate this connection and as the
main result we show that if $A$ is a universal $\textrm{GE}_2$-domain such that
$-1 \in A^{\times 2}$, then we have the exact sequence
$H_3(\textrm{SM}_2(A),\mathbb{Z}) \to H_3(\textrm{SL}_2(A),\mathbb{Z}) \to
\mathcal{RB}(A) \to 0$, where $\textrm{SM}_2(A)$ is the group of monomial
matrices in $\textrm{SL}_2(A)$. Moreover we show that $\mathcal{RP}_1(A)$, the
refined scissors congruence group of $A$, naturally is isomorph with the
relative homology group $H_3(\textrm{SL}_2(A), \textrm{SM}_2(A),\mathbb{Z})$.
