All God-Machine Infrastructure has a Linchpin. The Linchpin doesn't have to be tied by human logic to what the infrastructure does, thought there is often some symbolism or anti-logic to it.
Some examples of infrastructure in the book:
- An underground facility has three obelisks above it: one hides the air vents, one hides the power conduits, and one is just solid brick like it looks. The solid brick one is the linchpin.
- A bridge is infrastructure. Its linchpin is the pay-phone booth on the end.
Now in the sample adventure in the back of the book, it seems clear that demons can at least work out what the linchpin is, though not at a glance. However I can't find the rules to determine how it is done.
It is debatable whether infrastructural can be permanently destroyed without destroying the linchpin (or using a super-natural; ability like Destroy Infrastructure). It is quiet likely that any damage that doesn't destroy the linchpin can be repaired without requiring a new Occult Matrix to form it.
If there are no rules given, I lean towards a house rule like:
If you have Aesthetic Resonance active, then you may as a extended action, 1 minute/roll (longer for larger infrastructure), roll Wits + Science + Primum − penitences for concealment infrastructure, etc., to determine which part of the infrastructure is allowing it to work beyond the laws of known science.