I want to show that
$M$ is $A$-flat is equivalent to $\mathrm{Tor}_1^A(M,A/I)=0$ for every finitely generated ideal $I$.
I want to show $\mathrm{Tor}^A_1(M,N)=0$ for any $A$-module $N$.
Is every module a direct limit of $A/I$ described above? (If this holds, we can pass from $\mathrm{Tor}^A_1(M,A/I)=0$ to $\mathrm{Tor}^A_1(M,N)=0$ by taking direct limit.)
$\mathrm{Tor}_1^A(M,A/I)=0$ is equivalent to the following: the canonical homomorphism $I\otimes_AM\to M$ (that is, $a\otimes m\mapsto am$) is injective, and this is Theorem 7.7 from Matsumura, Commutative Ring Theory.