Concept wise:
cross_index=find(data1==data2);
This may not work, if there may floating numbers, in that case you may follow the following approximate
diff_data=data1-data2; %cross points might be zero or near by zero
indices_cross=find(diff_data>-th I diff_data<th);
Here th is minimal threshold value, which ensures all cross points having not exactly zero or nearby zero.
Other standard function also there, see the zero crossing functionsm you may get the idea.
